THESISMaterial Characterization Techniques for Microwave Imaging ApplicationsThe PhD research work is focused on a microwave and terahertz imaging using novel source antenna designs in order to study the dielectric material characterization of objects in both frequency and time domain. Initially, a novel shaped horn antennas are designed to improve the spot focusing characteristics at microwave and terahertz frequencies. A waveguide-horn-waveguide structure scheme is used to model a horn antenna in order to avoid lens correction over horn apertures, which is usually needed to enhance the spot focusing. The horn antennas are designed and simulated with an accurate proprietary Body-of-Revolution Finite-Element code. Later on, an interaction of electromagnetic waves with the material is studied, where the variation in magnitude and phase of the wave has been observed with and without the presence of a dielectric medium. After that, the accuracy of frequency and time domain systems evaluated for various dielectric properties, and different scattering response inversion techniques are developed and tested e.g, Fourier inversion and Bayesian inversion. Time and computation efficient post processing techniques have been developed in MATLAB to extract the dielectric properties, however, scattering parameters were obtained using commercial software (Ansys HFSS and CAD FEKO) as well. The measurement techniques majorly focused on the free space reflection response from the dielectric material with unknown electrical length. A new measurement has also been developed and tested for accurate scattering parameters extraction. Different Vector Network Analyzer (VNA) calibration technique e.g, TRL, waveguide etc. are carried out to minimise the measurement errors Latter, the thickness tolerance is also included in MATLAB post processing to reduce possible errors between ground (reference) and medium scattering measurements. The materials tested have the dielectric constant range from 2 to 50 with physical length range from 0.5mm to 10mm. The measurements are carried out at three different frequency ranges 20-40GHz, 75-110GHz and 915-925GHz. The possible applications of this research are biomedical imaging for detection and diagnoses of cancer, nondestructive testing of structural defects in objects, security scanning at airports and communication systems with ultra-high data rates.Advisor: Prof. Gian Guido Gentili

MINOR RESEARCHCompact Antenna Test Range for High-Frequency Satellite Antenna MeasurementsA compact antenna test range has been designed to be installed in the microwave/millimeter wave anechoic chamber (MAC) present in the Department of physics at the Università degli di Studi Milano. The design is based on a dual reflector cassegrain system, a compact range with this design will allow testing the far-field characteristics of telecommunication antennas, small telescopes, and payloads for scientific satellites. The performance parameters such as reflector rim dimensions, a shape of serrations, source feed taper, and distance of antenna under test in quiet zone axis have been analyzed with a parametric studied carried out using TICRA Grasp v10.2.0. This design is going to be manufactured with the typical techniques used for ground station antennas.Advisor: Prof. Gian Guido Gentili and Prof. Enrico Pagana